1. Field of the Invention
The present invention relates to organopolysiloxane compositions containing polyacyloxysilanes which cure very quickly into elastomeric state, when heated in the presence of an accelerator containing a 2-carboxycarboxamide group.
The compositions of the invention are members of the group of silicone elastomer compositions designated as "autoaccelerated cure".
2. Description of the Prior Art
Most of the autoaccelerated compositions known to this art are of the two-component (two-pack) type.
In contrast to the known single-component compositions which are cured by atmospheric moisture and which also bear acyloxy radicals bonded to silicon atoms (described, in particular, in French Pat. Nos. 1,198,749, 1,220,348, 2,429,811 and published French Patent Application No. 82/13,505, filed July 30, 1982), these compositions are not stable in storage, but their cross-linking time is much shorter, for example, on the order of a few minutes and up to 60 minutes. These known autoaccelerated compositions must therefore be prepared at the point in time of actual use.
The compositions of the above type, which have a short cross-linking time, such cross-linking being independent of the moisture content of the surrounding atmosphere, are used for those applications in which this property is especially advantageous, such as, for example, the manufacture of "in situ" seals in the automotive industry. Compositions of the above-mentioned type, bearing acyloxy radicals bonded to silicon atoms, whose cross-linking time is dependent of the moisture in the surrounding air, are known from French Pat. No. 1,193,721, in which the accelerator is zinc oxide, and from British Pat. No. 1,308,985, which '985 patent describes a curing process consisting of adding to the compositions 3 to 15% of a silicoaluminate cure accelerator containing from 5 to 10% by weight of absorbed water, in order to manufacture molded articles of a silicone elastomer by low-pressure injection molding.
Published French Patent Applications Nos. 2,540,128 and 2,540,129, filed Jan. 27, 1983, also describe compositions of this type, but in which the cure accelerator is selected, respectively, from an alkali metal and alkaline earth metal hydroxide, or from a mixture consisting of water and an alkali or alkaline earth metal phosphate and/or polyphosphate.
The accelerators described in both of these French applications mark a noted advance in this art relative to the teachings of French Pat. No. 1,193,721 and British Pat. No. 1,308,985, in the sense that, on the one hand, the nature and the amounts of accelerators which are added do not detract from the mechanical properties of the elastomer produced, especially with regard to residual compression set (RCS) and, on the other hand, these accelerators have made it possible to use such compositions for the bonding and sealing of components travelling on industrial assembly lines or those for which there are no available storage areas that would ensure their complete cure.
However, the compositions described in these patents cannot be produced in single-pack (single-component) form and must be packaged as two components: generally, on the one hand, the organopolysiloxane component and, on the other hand, the accelerator, because the mixture of these components must be made ad hoc, that is to say, at the point in time of actual use.
This procedure has disadvantages. First of all, there is of course a risk that the two components may not be measured out correctly at the time of use. In addition, especially in the case of the automatic production of "shaped" or "in situ" seals, the mixture is produced in a complex and costly automatic device for applying the compositions, which has a mixer head receiving the polysiloxane composition and the accelerator. The compositions used in this apparatus must then have a curing time which is properly adjusted to avoid setting in the mixer head, and this requires meticulous, time-consuming development. Furthermore, these mixer heads must be emptied in the event of a stoppage or a breakdown of the apparatus, to avoid setting.
A solution has been provided in published French Patent Application No. 2,553,784, which makes it possible to obtain single-component, autoaccelerated compositions which are stable in storage at ambient temperature in the absence of atmospheric moisture, by microencapsulating the accelerator. This microencapsulation is completely effective, but increases the cost of the compositions due to the additional microencapsulation step.